Yeah, we mostly have "it's good to buy me all the time" items and "I'm a good buy if I synergise with you enough to make up for not being generally good" items. This structure means that new items in the first category just raise the power level across the board (League of Cleavers was a fun time to be), and new items in the second category barely see play (Essence Reaver, Runaan's Hurricane, Banner of Command, I can go on). It's even worse when the strong items aren't universally good. Then you get champions who synergise with the item becoming dominant.
Half of the itemization issues can be fixed by flattening power curves. Infinity Edge and Rabadon's Deathcap do what their competitors do and more, instead of specifically focusing on powerful basic attacks and boosting non-damage AP ratios respectively. Randuin's doesn't need to give more physical defense than pure Armor items since it gives defense against magic damage as well, and it doesn't even pay for it besides having a pretty bad build path (actually noticing a pattern here; a lot of the really strong items have bad build paths).
The other half are items that are just badly designed due to being niches that are too small. This leaves the items either being good on everyone but abusive on a few, or good on a few but useless on everyone else. Grail is supposed to give champions with mana issues a way to compete when faced against champions lacking resource management, but it can screw up resource management itself on anyone whose mana issues are minor (plus 20% CDR really isn't needed). Runaan's Hurricane is supposed to give basic attackers who lack AoE damage a way to wave clear if they need to, but it synergises too well with one type of damage (on hits) and ignores another (crit chance) to compensate, leaving the standard basic attackers sacrificing too much damage and on hit dependent basic attackers gaining too much damage.
Supports face a different problem, and that's their gold income. They get an item to generate gold, but it's being spent on upgrading itself, then a Sightstone. Supports buying more items is technically possible, but it's far easier to just default to the old "pick whoever gets by the best with no gold" than to change the meta. Whee.